The exemplary embodiments relate to a method for adjusting frequency for a surface acoustic wave device using a pseudo-longitudinal leaky surface acoustic wave, the surface acoustic wave device, and an electronic device having the surface acoustic wave device.
In the related art, the resonance frequency of a surface acoustic wave element depends on the effective film thickness of an interdigitated (IDT) electrode or a reflector electrode (hereinafter, “an IDT electrode or a reflector electrode” is referred to as an electrode). The frequency increases as the electrode film thickness becomes small while the frequency decreases as the electrode film thickness becomes large. The frequency of a surface acoustic wave device is adjusted in the related art by using this principle.
For example, the method to adjust the frequency by trimming an electrode to be thin is disclosed in a first example of the related art. The related art includes another frequency adjustment method (second example of the related art), wherein instead of thickening an electrode, the apparent electrode film thickness is increased by trimming a substrate using an electrode as a mask.
In recent years, as the usage of communication devices expands, higher frequency of surface acoustic wave devices and more accurate adjustments of frequency are desired. It is particularly expected that a pseudo-longitudinal leaky surface acoustic wave can be used for higher frequency of surface acoustic wave devices. This wave is expected to result from expansion according to the theory of leaky surface acoustic waves. Further, this wave has displacement, most of which is composed of longitudinal wave components, on the substrate surface, and propagates at a fast phase velocity while radiating two transverse wave components as volume waves inside a piezoelectric substrate. It is expected that particularly using lithium tantalite (LiTaO3), lithium niobate (LiNbO3), and lithium tetraborate (Li2B4O7), which have high electromechanical coupling coefficients, as substrate materials will achieve a higher frequency of surface acoustic wave devices. See Japanese Unexamined Patent Publication No. Sho 62-274081 and Japanese Unexamined Patent Publication No. Sho 61-92011.
As described above, in related art frequency adjustments of surface acoustic waves, an electrode or a substrate surface on which the electrode is formed has been trimmed by a method, such as etching. However, the frequency change with respect to the etching amount is large, and therefore adjusting frequency with high accuracy is difficult. Particularly in the surface acoustic wave devices that use pseudo-longitudinal leaky surface acoustic waves to strive for higher frequency, the frequency change with respect to the etching amount is even larger, and therefore attaining a more accurate frequency adjustment is a problem for practical applications.